Patients suffering from Chronic Heart Failure (CHF) are hospitalized for acute heart failure (AHF) several times a year. Currently, we have no method for prediction of future developments of AHF. In our center we have investigated the monitoring of lung impedence as a predictor for future deterioration. It was found that a decrease in lung impedence of more than 15% from normal value predicts AHF development with sensitivity of 98%. In this study we try to prove the hypothesis that preventive treatment according to lung impedence value may prevent future hospitalizations for AHF and improve clinical outcome.